Update some error messages in statistics

Relevant PG commits:
https://github.com/postgres/postgres/commit/ab16418ee
https://github.com/postgres/postgres/commit/f225473cb
https://github.com/postgres/postgres/commit/f9b41f3e1

src/test/regress/expected/pg18_0.out

@@ -8,12 +8,12 @@ SELECT substring(:'server_version', '\d+')::int >= 18 AS server_version_ge_18
 -- behavior is same among PG versions, error message differs
 -- relevant PG18 commit: 3eea4dc2c7, 38883916e
 CREATE STATISTICS tst ON a FROM (VALUES (x)) AS foo;
-ERROR:  only a single relation is allowed in CREATE STATISTICS
+ERROR:  CREATE STATISTICS only supports relation names in the FROM clause
 CREATE FUNCTION tftest(int) returns table(a int, b int) as $$
 SELECT $1, $1+i FROM generate_series(1,5) g(i);
 $$ LANGUAGE sql IMMUTABLE STRICT;
 CREATE STATISTICS alt_stat2 ON a FROM tftest(1);
-ERROR:  only a single relation is allowed in CREATE STATISTICS
+ERROR:  CREATE STATISTICS only supports relation names in the FROM clause
 DROP FUNCTION tftest;
 \if :server_version_ge_18
 \else

src/test/regress/expected/propagate_statistics.out

@@ -16,7 +16,7 @@ SELECT create_distributed_table('test_stats', 'a');
 (1 row)
 
 CREATE STATISTICS pg_temp.s1 (dependencies) ON a, b FROM test_stats;
-ERROR:  "statistics object s1" has dependency on unsupported object "schema pg_temp_xxx"
+ERROR:  "statistics object pg_temp_xxx.s1" has dependency on unsupported object "schema pg_temp_xxx"
 CREATE STATISTICS s1 (dependencies) ON a, b FROM test_stats;
 -- test for distributing an already existing statistics
 CREATE TABLE "test'stats2" (